Film-packed battery and method of manufacturing the same

ABSTRACT

A film-packed battery includes a battery element and a packing film which houses the battery element and includes a main heat-sealed portion which is formed around the battery element, and a projecting heat-sealed portion which projects from the main heat-sealed portion toward the battery element, and a gas releasing portion formed in the projecting heat-sealed portion and the main heat-sealed portion adjacent to the projecting heat-sealed portion, wherein a distal end of the gas releasing portion reaches the projecting heat-sealed portion and the gas releasing portion connects external air with a heat-sealed interface of the packing film.

RELATED APPLICATIONS

The present Application claims priority to Japanese Patent ApplicationNo. 209847/2002 filed on Jul. 18, 2002, and International ApplicationNo. PCT/JP03/09029 filed on Jul. 16, 2003, and is a ContinuationApplication of U.S. patent application Ser. No. 10/512,844 which wasfiled on Oct. 29, 2004, and issued as U.S. Pat. No. 7,901,806 on Mar. 8,2011.

BACKGROUND OF THE INVENTION

The present invention relates to a film-packed battery in which abattery element is stored in a film packing body and a method ofmanufacturing the same and, more particularly, to a film-packed batterywhich can appropriately cope with gas generation in an abnormality, anda method of manufacturing the same.

In recent years, strong demands have arisen for lower-weight,lower-profile batteries as power supplies for portable devices and thelike. Regarding a battery packing body, in place of a conventional metalcan case which is limited in weight reduction and profile reduction, ametal thin film or a laminated film formed of a metal thin film and aheat sealable resin film has been in use as a packing body which can bereduced in weight and profile and can take an arbitrary shape whencompared to a metal can case.

As the laminated film, one which includes a metal thin film made ofaluminum and a heat sealable resin film made of nylon to form a batteryouter surface and polyethylene or polypropylene to form a battery innersurface is generally used. A cathode, an anode, and a battery elementmade of an electrolyte are stored in a packing body formed of thelaminated film. The periphery of the packing body is heat-sealed.

Most of batteries that use metal can case as general packing bodies havea pressure safety valve which, when a gas is generated at the time of anabnormality and the pressure in the battery increases, releases the gasto the outside.

In a film-packed battery which uses a film as a packing body, however,it is difficult to provide a pressure safety valve due to the structure.When an abnormality occurs, the packing body expand to the limit withthe generated gas. It is unknown where the packing body may rupture toblow the gas into the equipment, leading to an issue.

Japanese Patent Laid-Open No. 2000-100399 proposes a means with whichpart of the heat-sealed portion is sealed at a low temperature to form asafety valve. Japanese Patent Laid-Open No. 11-097070 proposes a meanswith which a non-heat-sealable resin sheet is interposed and heat-sealedto decrease the peeling strength, thus forming a safety valve. With theabove means, however, the sealing reliability also decreases in a normalstate where the pressure does not increase. Then, the seal portion isdeteriorated, and inconveniences such as leakage of an electrolyte mayoccur. Also, the pressure for opening the safety valve at the time of anabnormality cannot be set accurately. Japanese Patent Laid-Open No.2001-325926 disposes a scheme of forming a recessed groove in alaminated sheet and releasing the generated gas outside the battery.Even with this proposal, it is cumbersome to form the recessed groove,and the laminated sheet must be welded to an opposing laminated sheet intwo steps. Accordingly, very cumbersome operations are needed.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a film-packedbattery in which an accurate unsealing pressure necessary when thebattery expands by gas generation in an abnormality can be set, and amember that serves as a pressure safety valve having a sealingreliability which does not deteriorate the battery characteristics innormal use can be provided easily.

A film-packed battery according to the present invention ischaracterized by comprising a cathode, an anode, a battery element madeof an electrolyte, a packing film which stores the battery element andsealed by heat-sealing part of a bonding surface thereof around thebattery element, a projecting heat-sealed portion formed in part of aheat-sealed portion by heat seal to project toward the battery element,and a gas releasing portion formed in at least one of the projectingheat-sealed portion and a heat-sealed portion adjacent thereto.

A method of manufacturing a film-packed battery according to the presentinvention is characterized by comprising the steps of storing a batteryelement in a packing film, sealing a bonding surface of the packing filmaround the battery element by heat seal, forming, in part of aheat-sealed portion by heat seal simultaneously with heat seal of thebonding surface, a projecting heat-sealed portion which is continuoustoward the battery element, and forming a gas releasing portion in atleast one of the projecting heat-sealed portion and a heat-sealedportion adjacent to the projecting heat-sealed portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the appearance of a film-packedbattery according to the first embodiment of the present invention;

FIG. 2 is a longitudinal sectional view taken along the line A-A of FIG.1;

FIG. 3 is a perspective view in which the heat-sealed portion andprojecting heat-sealed portion of the film-packed battery of FIG. 1 arehatched;

FIG. 4 is an exploded perspective view of the film-packed battery ofFIG. 1;

FIG. 5 is a perspective view showing the appearance of a film-packedbattery according to the second embodiment of the present invention;

FIG. 6 is a perspective view showing the appearance of a film-packedbattery according to the third embodiment of the present invention;

FIGS. 7A and 7B are perspective views showing the appearance of afilm-packed battery according to the fourth embodiment of the presentinvention;

FIG. 8 is a perspective view showing the appearance of a film-packedbattery according to the fifth embodiment of the present invention;

FIG. 9 is a perspective view showing the appearance of a film-packedbattery according to the sixth embodiment of the present invention;

FIG. 10 is a perspective view showing the appearance of a film-packedbattery according to the seventh embodiment of the present invention;

FIG. 11 is a perspective view showing the appearance of a film-packedbattery according to the eighth embodiment of the present invention;

FIG. 12 is a perspective view showing the appearance of a film-packedbattery according to the ninth embodiment of the present invention; and

FIG. 13 is an exploded perspective view of a film-packed battery in alaminated state according to an embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be described withreference to the drawings.

First Embodiment

The first embodiment of the present invention will be described withreference to FIGS. 1, 2, 3, and 4. As shown in FIG. 4, a film-packedbattery 1 has a packing body 2 storing a battery element 9, and acathode lead terminal 3 and anode lead terminal 4 which are connected tothe battery element 9 and project outside the packing body 2.

As shown in FIG. 2, the packing body 2 includes an upper film 8 a andlower film 8 b. The two films 8 a and 8 b are heat-sealed around thebattery element 9, as hatched in FIG. 3, to form a heat-sealed portion5, and are bonded to each other.

A projecting heat-sealed portion 6 projecting toward the battery element9 is continuously formed at the center of that side of the heat-sealedportion 5 where the cathode lead terminal 3 and anode lead terminal 4are formed. A triangular gas releasing portion 7, the distal end ofwhich reaches the projecting heat-sealed portion 6, is also formed. Thegas releasing portion 7 has a function of allowing external air and theheat-sealed film interface to communicate with each other.

The projecting heat-sealed portion 6 can be formed, simultaneously withthe heat-sealed portion 5, by heat seal when sealing the periphery ofthe packing body. Hence, the projecting heat-sealed portion 6 can beformed without requiring any particular step. Also, the projectingheat-sealed portion 6 can be heat-sealed with the same strength as thatof the heat-sealed portion 5 on the periphery of the packing body 2.Thus, for example, leakage of an electrolyte does not occur, and thereliability of the pressure safety valve is not degraded when comparedto the other heat-sealed portion 5.

As shown in FIG. 3, the gas releasing portion 7 of this embodiment isformed by setting up a portion that is not to be heat-sealed. If aheat-sealing head used for heat seal has such a shape that it heat-sealsthe projecting heat-sealed portion 6 but does not heat-seal the gasreleasing portion 7 of the heat-sealed portion 5, the gas releasingportion 7 and projecting heat-sealed portion 6 can be formed easily.

As described above, according to this embodiment, the projectingheat-sealed portion 6 projecting toward the battery element is formed inpart of the heat-sealed portion around the battery. When the packingbody expands with gas generation in the case of an abnormality, a stressin a peeling direction concentrates at the projecting heat-sealedportion 6. The heat-sealed portion selectively peels off the projectingheat-sealed portion 6.

When peeling reaches the gas releasing portion 7 which is close to theprojecting heat-sealed portion 6 and communicates with the external airsuch that the films 8 a and 8 b forming the packing body 2 are notheat-sealed to each other, the interior of the battery and the externalair communicate with each other to release the gas in the batteryoutside, and rupture of the battery or blowing of the gas in anunintended direction is prevented. This function is called the functionof the pressure safety valve.

Second and Third Embodiments

The second and third embodiments of the present invention will bedescribed with reference to FIGS. 5 and 6.

According to the second embodiment, as shown in FIG. 5, the shape of agas releasing portion 7 a with a distal end that reaches a projectingheat-sealed portion 6 is different from that of the first embodiment.The gas releasing portion 7 a is formed not from a non-heat-sealedportion but from a linear incision that reaches the projectingheat-sealed portion 6 from the edge of a packing body 2.

The incision may be formed before or after the heat-sealing step. Whenthe incision is to be formed before the heat-sealing step, it may beformed in only one of opposing films. In this embodiment, when thepacking body expands with gas generation in an abnormality, a stress ina peeling direction concentrates at the projecting heat-sealed portion6. The heat-sealed portion 5 selectively peels off the projectingheat-sealed portion 6, and the internal gas is released outside throughthe gas releasing portion 7.

According to the third embodiment, as shown in FIG. 6, a gas releasingportion 7 b is formed of an acute triangular notch with a distal endthat reaches a projecting heat-sealed portion 6. In this embodiment, thestress generated by the generated gas concentrates at the projectingheat-sealed portion 6, and the generated gas is released outside throughthe gas releasing portion 7 b. Thus, rupture of the battery or spurt ofgas in an unintended direction is prevented.

Fourth Embodiment

The fourth embodiment of the present invention will be described withreference to FIGS. 7A and 7B.

According to the fourth embodiment, as shown in FIG. 7A, a gas releasingportion 7 c is formed as a hole formed in a projecting heat-sealedportion 6. It suffices as far as this hole is formed in at least one oftwo opposing films. Alternatively, this hole may be one that extendsthrough the two opposing films, in the fourth embodiment, in the samemanner as in other embodiments, a gas that can be generated in a batterypeels the two films of the projecting heat-sealed portion 6, and isreleased outside through the gas releasing portion 7 c formed as thehole. Alternatively, the film-packed battery 1 may include pluralprojecting portions 6, and plural gas releasing portions 7 c, asillustrated in FIG. 7B.

Fifth Embodiment

The fifth embodiment of the present invention will be described withreference to FIG. 8.

As shown in FIG. 8, the eighth embodiment is different in that aprojecting heat-sealed portion 6 d and gas releasing portion 7 d areformed not between cathode and anode lead terminals 3 and 4, as in thefirst to fourth embodiment, but on the cathode lead terminal 3. Thebonding strength of a heat-sealed portion 5 is generally lower at thebonding portions of films and lead terminals than at the bondingportions of films. When the projecting heat-sealed portion 6 d and gasreleasing portion 7 d are formed on the cathode lead terminal 3, thevalve unsealing pressure can be set low.

Although the projecting heat-sealed portion 6 d and gas releasingportion 7 d are formed on the cathode lead terminal in FIG. 8, they canbe formed on the anode lead terminal 4. The whole projecting heat-sealedportion 6 d need not be located on the cathode lead terminal 3, but itmay be partially located on the cathode lead terminal.

Sixth Embodiment

The sixth embodiment of the present invention will be described withreference to FIG. 9.

As shown in FIG. 9, the sixth embodiment is different in that aprojecting heat-sealed portion 6 e and gas releasing portion 7 e areformed neither between cathode and anode lead terminals 3 and 4, as inthe first to fourth embodiments, nor on the cathode lead terminal 3, asin the fifth embodiment, but on the corner of the packing body.

The projecting heat-sealed portion may be formed at an arbitraryposition on the periphery of the packing body. Considering a batteryelement 9 and arrangement of the electrode lead terminals 3 and 4, theprojecting heat-sealed portion is desirably formed at a location whereit does not adversely affect the outer shape of the battery. When theprojecting heat-sealed portion 6 e and gas releasing portion 7 e areformed at the corner of the packing body, as in this embodiment, thesame effect can be obtained.

Seventh Embodiment

The seventh embodiment of the present invention will be described withreference to FIG. 10.

According to this embodiment, the external-air-side end of a gasreleasing portion 7 formed as in the first embodiment is heat-sealed toform a seal portion 13. When the seal portion 13 is formed, externaldust or the like can be prevented from clogging in the gas releasingportion 7 to hinder the operation of the pressure safety valve, or thegas releasing portion 7 can be prevented from forming an entry path forwater vapor into the battery from outside to degrade batterycharacteristics.

The seal portion 13 must be sealed with a low strength that does notinterfere with gas releasing when the seal portion 13 operates as apressure safety valve. In FIG. 10, the seal portion 13 is formed by heatseal with a smaller width than that of the other heat-sealed portions 5.To decrease the bonding strength, the seal portion 13 may be formed bydiffusion with a lower temperature than for the other heat-sealedportion 5.

Eighth Embodiment

The eighth embodiment of the present invention will be described withreference to FIG. 11.

According to this embodiment, unlike in the seventh embodiment, a sealportion 13 a is formed of an adhesive applied to the inner side of a gasreleasing portion 7. Any other known method such as filling with athermosetting resin may be used. The adhesive or resin desirably adhereswith a small force so that it will not interfere with gas releasing whenthe seal portion 13 a operates as a pressure safety valve.Alternatively, an adhesive or resin which is dissolved or decomposed bya battery element 9 component such as an electrolyte may be used.

Ninth Embodiment

The ninth embodiment of the present invention will be described withreference to FIG. 12.

According to this embodiment, unlike in the seventh and eighthembodiments, a gas releasing portion 7 (shown by a dotted lined iscovered with a tape to form a seal portion 13 b. When a tape or seal isused, the seal portion 13 b can be easily formed on the gas releasingportion 7. As the tape, a laminated film including a metal foil or metalthin film may be used. To bond the tape, a known method such as one thatuses a pressure-sensitive adhesive, adhesive, or heat seal can beemployed.

In each one of FIGS. 1 to 12, one projecting heat-sealed portion and onegas releasing portion are formed. Alternatively, two or more projectingheat-sealed portions and two or more gas releasing portions may beformed at arbitrary locations.

The arrangement and movement of a film-packed battery according to thepresent invention will described as an embodiment.

(Fabrication of Cathode)

A lithium manganate powder having a spinel structure, a carbonaceousconductivity imparting material, and polyvinylidene fluoride were mixedand dispersed in NMP (N-methyl-2-pyrrolidone) with a weight ratio of90:5:5. The mixture was stirred to form a slurry. The amount of NMP wasadjusted such that the slurry had an appropriate viscosity. Using adoctor blade, the slurry was uniformly applied to one surface of a 20-μmthick aluminum foil as a prospective cathode collector. Application wasperformed such that uncoated portions (portions where the collector wasexposed) were slightly formed as stripes.

Subsequently, the resultant aluminum foil was dried at 100° C. in vacuumfor 2 hrs. The slurry was similarly applied to the other surface, andthe aluminum foil was dried in vacuum such that the uncoated portions onthe front and rear surfaces coincided. The obtained sheet, the twosurfaces of which were coated with an active material in this manner,was rolled with a press. The resultant sheet was cut into a rectangle toinclude the uncoated portions, thus forming a cathode plate 10. Theactive-material-uncoated portion was cut out to leave rectangularportions on its one side. The left portions were used as lead portions.

(Fabrication of Anode)

An amorphous carbon powder and polyvinylidene fluoride were mixed anddispersed in NMP with a weight ratio of 91:9. The mixture was stirred toform a slurry. The amount of NMP was adjusted such that the slurry hadan appropriate viscosity.

Using a doctor blade, the slurry was uniformly applied to one surface ofa 10-μm thick copper foil as a prospective anode collector. Applicationwas performed such that uncoated portions (portions where the collectorwas exposed) were slightly formed as stripes. Subsequently, theresultant aluminum foil was dried at 100° C. in vacuum for 2 hrs.

The thickness of the active material layer was adjusted such that theratio of theoretical capacitance per unit area of the anode layer to thetheoretical capacitance per unit area of the cathode layer was 1:1.Similarly, the slurry was applied to the other surface, and the aluminumfoil was dried in vacuum. The obtained sheet, the two surfaces of whichwere coated with the active material in this manner, was rolled with apress. The resultant sheet was cut into a rectangle including theuncoated portions, such that the rectangle was larger than the cathodeby 2 mm in each of the vertical and horizontal sizes, thus forming acathode plate 11. The active-material-uncoated portion was cut out toleave rectangular portions part on its one side. The left portions wereused as lead portions.

(Fabrication of Battery Element)

The cathode and anode fabricated in the above manner, and microporousseparators each having a three-layered structure ofpolypropylene/polyethylene/polypropylene were alternately stacked. Asshown in FIG. 13, anodes appeared on the outermost sides of theelectrodes, and separators were further placed on the outer side of theanodes (in the order of separator 12/anode 11/separator 12/cathode10/separator 12/ . . . /anode 11/separator 12).

An aluminum plate was ultrasonic-welded to serve as a cathode plate leadand cathode lead terminal 3 for the stacked cathodes at once. Similarly,a nickel plate was ultrasonic-welded to serve as an anode lead And anodelead terminal 4 at once.

(Fabrication of Film-Packed Battery)

Fabrication of a film-packed battery will be described with reference toFIG. 4.

A storing portion having a size much larger than that of a batteryelement 9 was formed by deep drawing in a film 8 a serving as analuminum laminated film having a three-layered structure ofnylon/aluminum/polypropylene, such that the polypropylene side wasrecessed.

The above battery element 9 was stored in the battery element storingportion of the film 8 a such that only a cathode lead terminal 3 andanode lead terminal 4 of the battery element 9 projected from thepacking film body. The battery element 9 was covered with another film 8b. The bonding portions were overlaid, and the three sides on theperiphery of the packing body were bonded by heat seal. Regarding aheat-sealed portion 5 on a side from which the lead wires extend, it wasbonded with a heat-sealing machine having a heat-sealing head which wasto form, between the cathode and anode lead terminals, a projectingheat-sealed portion 6 projecting toward the battery element 9 and a gasreleasing portion 7 formed of a non-diffused portion that reached theouter periphery of the heat-sealed portion 5 from the projectingheat-sealed portion 6.

An electrolyte was injected into the storing portion of the batteryelement 9 from one remaining side that was not been bonded. Theelectrolyte contained 1 mol/L of LiPF6 as support salt and a mixedsolvent of propylene carbonate and ethylene carbonate (weight ratio of50:50) as a solvent. After injecting the electrolyte, the packing bodywas sealed in vacuum. A lithium ion secondary battery having a laminatedfilm packing body was obtained.

The projecting heat-sealed portion is continuous to the heat-sealedportion and can be formed in one process simultaneously with formationof the heat-sealed portion. Hence, not only the work efficiency isimproved, but also the heat-sealing strengths of the heat-sealed portionand projecting heat-sealed portion become substantially equal. Then, thegas generated inside reliably promotes peeling off the projectingheat-sealed portion. As a result, gas spray in an unintended directionis prevented reliably.

The gas releasing portion has a function of releasing the gas inside thebattery when peeling of the projecting heat-sealed portion 6 due to theexpansion of the packing body upon pressure increase has progressed to aregulated portion. The gas releasing portion may be present at theprojecting heat-sealed portion or the heat-sealed portion adjacent toit, or across the projecting heat-sealed portion and heat-sealedportion.

(Operation of Pressure Safety Valve)

In the film-packed battery 1, upon occurrence of an abnormality such asexternal short-circuiting, when the temperature in the battery increasessharply and the packing body 2 expands due to gas generation, the stressgenerated by the expansion concentrates at the projecting heat-sealedportion 6. Hence, peeling of the heat-sealed portion 5 progressesselectively at the projecting heat-sealed portion 6. When peelingreaches the gas releasing portion 7, the interior of the battery and theexternal air communicate with each other. The gas generated in thebattery is then released outside through the gas releasing portion 7.

The actuating pressure as the safety valve can be set arbitrarily inaccordance with the positions and shapes of the projecting portion 6 andgas releasing portion 7. Furthermore, in a normal state with no gasgeneration, the same reliability as that of the other heat-sealedportion 5 can be maintained.

According to the embodiments described above, a heat-sealed portionprojecting toward a battery element is formed, and a gas releasingportion is formed close to the projecting heat-sealed portion. Then,when the pressure in the battery increases upon gas generation, peelingof the projecting heat-sealed portion progresses selectively, andpeeling reaches as far as the gas releasing portion. As a result, thegas in the battery can be released outside.

A film-packed battery in which the valve unsealing pressure can bearbitrarily set in accordance with the positions and shapes of theprojecting heat-sealed portion and gas releasing portion and which has afunction of a pressure safety valve having a high sealing reliability innormal use can be provided easily.

As described above, a film-packed battery according to the presentinvention in which a battery element is stored in a film packing body,and a method of manufacturing the same are suitably used in a powersupply for a portable equipment or the like.

1. A film-packed battery comprising: a battery element; a packing filmwhich houses the battery element and includes: a main heat-sealedportion which is formed around said battery element; and a projectingheat-sealed portion which projects from said main heat-sealed portiontoward said battery element; and a gas releasing portion formed in atleast one of said projecting heat-sealed portion and said mainheat-sealed portion, wherein a distal end of said gas releasing portionreaches said projecting heat-sealed portion and said gas releasingportion connects external air with a heat-sealed interface of saidpacking film.
 2. The film-packed battery according to claim 1, whereinsaid gas releasing portion is formed at that portion of said heat-sealedportion which is not heat-sealed.
 3. The film-packed battery accordingto claim 1, wherein said packing film comprises: a first film formed ona side of said battery element; and a second film formed on another sideof said battery element, said first film being heat-sealed to saidsecond film in said main heat-sealed portion and said projectingheat-sealed portion.
 4. The film-packed battery according to claim 3,wherein said gas releasing portion comprises an incision that is formedin one of said first and second films and reaches said projectingheat-sealed portion.
 5. The film-packed battery according to claim 3,wherein said gas releasing portion comprises a notch that is formed inone of said first and second films and reaches said projectingheat-sealed portion.
 6. The film-packed battery according to claim 3,wherein said gas releasing portion comprises a hole formed in one ofsaid first and second films.
 7. The film-packed battery according toclaim 1, wherein said projecting heat-sealed portion and said gasreleasing portion are formed on a side from which electrode lead wiresextend.
 8. The film-packed battery according to claim 1, wherein saidprojecting heat-sealed portion and said gas releasing portion are formedin an electrode lead wire extending portion.
 9. The film-packed batteryaccording to claim 1, wherein said projecting heat-sealed portion andsaid gas releasing portion are formed at a corner of said packing film.10. The film-packed battery according to claim 1, wherein saidprojecting heat-sealed portion and said gas releasing portion are formedat substantially a center of a side of said packing film.
 11. Thefilm-packed battery according to claim 1, wherein said gas releasingportion includes a seal portion having a pressure resistance which isless than a pressure resistance of said main heat-sealed portionadjacent to said gas releasing portion.
 12. The film-packed batteryaccording to claim 11, wherein said seal portion is heat-sealed at atemperature lower than that for another heat-sealed portion.
 13. Thefilm-packed battery according to claim 11, wherein said seal portion hasa heat-sealing width less than a heat-sealing width of said adjacentmain heat-sealed portion.
 14. The film-packed battery according to claim11, wherein said seal portion is sealed with an adhesive or resin. 15.The film-packed battery according to claim 14, wherein said adhesive orresin is dissolved by at least one component of said battery element.16. The film-packed battery according to claim 14, wherein said adhesiveor resin is decomposed by at least one component of said batteryelement.
 17. The film-packed battery according to claim 11, wherein saidseal portion is formed by covering said gas releasing portion with atape or seal.
 18. The film-packed battery according to claim 1, whereinsaid projecting heat-sealed portion comprises plural projectingportions, and said gas releasing portion comprises plural gas releasingportions.
 19. The method of manufacturing a film-packed battery,comprising: storing a battery element in a packing film, comprising:forming a main heat-sealed portion which is formed around said batteryelement; and forming a projecting heat-sealed portion which projectsfrom said main heat-sealed portion toward said battery element; andforming a gas releasing portion, a distal end of which reaches saidprojecting heat-sealed portion, in at least one of said projectingheat-sealed portion and said main heat-sealed portion to connectexternal air with a heat-sealed interface of said packing film.
 20. Themethod of manufacturing a film-packed battery according to claim 19,wherein said forming the projecting heat-sealed portion by heat sealincludes forming, simultaneously with formation of the projectingheat-sealed portion, the gas releasing portion by not heat-sealing partof the heat-sealed portion.